Alumina ceramic lamp having enhanced heat conduction to the amalgam pool

Abstract

A high intensity sodium vapor lamp comprises a tubular envelope of alumina ceramic provided with end closures and containing a charge of sodium mercury amalgam in excess of that vaporized during operation. One closure includes a refractory metal tube sealed off at its tip and wherein unvaporized excess of amalgam collects as a liquid pool. In order to have a sufficiently high temperature at the amalgam pool, a metal slug of high heat conductivity such as molybdenum is placed in it and extends from the seal region towards the tip. Such slug also prevents overheating the seal between the ceramic tube and the end cap.

What we claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. A high pressure alkali metal vapor discharge lamp comprising: a slender light-transmissive ceramic tube having closures sealed to opposite ends and electrodes supported thereby; a filling of alkali metal in excess of the quantity vaporized in operation and an inert gas within said tube;   at least one of said closures comprising a metal tube extending hermetically therethrough;   said metal tube supporting the electrode at its inner end, having an opening into the ceramic tube, and being closed at its outer end to provide a reservoir for condensed alkali metal;   and metal of high heat conductivity enclosed within said metal tube and extending from the region of the end of the ceramic tube towards the closed end of said metal tube, said metal serving to raise the temperature of the amalgam condensed at the closed end of said metal tube.   
     
     
       2. A lamp as in claim 1 wherein said metal is a separate metal slug. 
     
     
       3. A lamp as in claim 2 wherein the metal tube is deformed to prevent movement of the metal slug within it. 
     
     
       4. A lamp as in claim 1 wherein a heat shield comprising a metal band having an emissivity less than said ceramic is wrapped around the end of the ceramic tube. 
     
     
       5. A lamp as in claim 1 wherein the closed outer end of said metal tube is roughened to increase its thermal emissivity and assure a well-defined cold spot. 
     
     
       6. A high pressure sodium vapor discharge lamp comprising: a slender light-transmissive ceramic tube having closures and electrodes supported thereby at opposite ends;   a filling of sodium-mercury amalgam in excess of the quantity vaporized in operation and an inert gas within said tube;   at least one of said closures comprising a metal end cap into which the end of the ceramic tube is sealed by sealing material and a metal tube extending hermetically through the end wall of said cap;   said metal tube supporting the electrode at its inner end, having an opening into the ceramic tube, and being closed at its outer end to provide a reservoir for condensed amalgam;   and a length of metal of high heat conductivity enclosed within said metal tube and extending from the region of the end of the ceramic tube towards the closed end of said metal tube, said metal serving to raise the temperature of the amalgam condensed at the closed end of said exhaust tube.   
     
     
       7. A lamp as in claim 6 wherein said length of metal is a separate metal slug. 
     
     
       8. A lamp as in claim 7 wherein said metal slug is of molybdenum. 
     
     
       9. A lamp as in claim 7 wherein the metal tube is deformed to prevent movement of the metal slug within it. 
     
     
       10. A lamp as in claim 7 wherein the metal tube is crimped to lock the metal slug within it and the slug is displaced toward the electrode. 
     
     
       11. A lamp as in claim 6 wherein a heat shield comprising a metal band having an emissivity less than said ceramic is wrapped around the end of the ceramic tube next to said metal end cap. 
     
     
       12. A lamp as in claim 6 wherein the closed outer end of said metal tube is roughened to increase its thermal emissivity and assure a well-defined cold spot.